1. Field of the Invention
The present invention relates to cemented carbonitride alloys containing titanium as a main component and tantalum, whose cutting property is markedly improved.
2. Description of the Prior Art
Titanium carbide base alloys of the prior art have hitherto been used for cutting tools excellent in wear resistance, in particular, for the high speed cutting of steels, because of not only their low production cost but also their excellent oxidation resistance at high temperatures and small chemical affinity to metals, but the scope of the intended use thereof is considerably limited because of the following three reasons. The first reason is that such a titanium carbide base alloy has a poor toughness and a tendency of breakage. It is known empirically that, when a tool is under the impulsive force of an interrupted cutting, etc., or when the rigidity of a machine tool is low, a titanium carbide base alloy is easier to break than a tungsten carbide base alloy of the prior art. The second reason by which the use of a titanium carbide base alloy is restricted is that deformation of an edge is large at a high temperature and high pressure. In a practical heavy cutting using an edge of titanium carbide base alloy, the edge meets an increase of temperature and a marked deformation and is not resistant to cutting. This is a main reason for the limited use of a titanium carbide base alloy to a light cutting operation. Furthermore, in the case of cutting a high hardness material, the temperature of an edge is markedly increased and, accordingly, a titanium carbide base alloy is not suitable for this case. The third disadvantage is that a titanium carbide base alloy is inferior to a tungsten carbide base alloy in thermal fatigue resisting property. Due to this disadvangage, a titanium carbide base alloy has not been used yet in operations with abnormal heat generations or loads, such as black cuttings or profiling cuttings varying in cutting depths, feeds, etc.
Various efforts have hitherto been made in order to overcome the above described three disadvantages. The latest proposal is to obtain a cemented carbonitride alloy of fine grain structure having an improved toughness and plastic deformation resistance at a high temperature by adding titanium nitride to titanium carbide base cermets of the prior art. In this alloy, the above described first and second disadvantages can be solved to some extent, but the third disadvantage is scarcely overcome. This constitutes a bar to the application of titanium carbide base or titanium carbonitride base cemented alloys to general use as a cutting tool.